Frequency responsive fluid switch

ABSTRACT

A frequency responsive fluid switching circuit including a fluidic AND gate and a delay line, for producing an output signal when the period of an applied fluid pulse train substantially equals the time delay of the delay line.

United States Patent Trull [151 3,704,719 [451 Dec. 5, 1972 [541 FREQUENCY RESPONSIVE FLUID SWITCH [72] Inventor: Gary E. Trull, Fridley, Minn.

[73] Assignee: Honeywell Inc., Minneapolis, Minn.

'[22] I Filed: June 18, 1970 [21] ApplqNo; 47,536

52] us. Cl ..137/81.5, 235/201 ME [51] Int. Cl ..-.....Fl5c l/l2, Fl5c 3/00 [58] Field of Search ..l37/81.5; 235/201 ME [56] 7 References Cited UNITED STATES PATENTS 3,531,985 10/1970 Martin l.l37/815 x 3,502,094 3/1970 Johnson ..l37/8l.5

3,552,414 l/1971 Sutton ..137/81.5

3,554,205 l/l97l Bellman ..l37/8l.5 3,557,813 l/197l Fegley et a1. ..137/81.5 3,559,665 2/1971 Davis et al ..137/8l.5

Primary Examiner-Samuel Scott Attorney-Charles J. Ungemach, Ronald T.' Reiling and Charles L. Rubow [57] 1 ABSTRACT A frequency responsive fluid switching circuit including a fluidic AND gate and a delay line, for producing an output signal when the period of an applied fluid pulse train substantially equals the time delay of the delay line.

3 Claims, 5 Drawing Figures PATENTEDnm 51922 B J 2 G I G F mm mm 4 m I 3 M 8 w 4 a M w w u fill a G s H l: 0 III ||l|l 4 p r r M. m M a SIGNAL AMPLITUDE FIG. 4

' NVENTOR.

GARY IE. muu.

BY FM! 742 FREQUENCY OUTPUT T A ATTORM FREQUENCY RESPONSIVE FLUID SWITCH BACKGROUND OF THE INVENTION tronic control systems.

In such fluidic control systems, it is sometimes desirable to monitor'the rotational. speed of a rotating member in a machine, and to provide fluid control signals if the rotational speed should exceed a predetermined value. For example, in a control system for a jet engine, it is necessary to providemeans for theprevention of an over-speed condition. An overspeed condition occurs when the rotational speed of the engines turbineexceeds a critical value, and if the engine is allowed to continue tooperate in an overspeed condition, permanent damage or destructionof the engine will result. Accordingly, it is desirable in such an engine control system to provide means for sensing the turbine speed, and for providing an output signal when the turbine speed exceeds a predetermined value. This output SUMMARY OF THE INVENTION Applicants invention comprises signal means for supplying a train of fluid pulses of variable frequency, fluid'AND gate means having two inputs and an output, and' means for transmitting the train of fluid pulses, with unequal time delays, from the signal means to the first and second inputs of the fluid AND gate. According to the applicants invention, an output signal from the AND gate will not be obtained when the frequency of the train of fluid pulses is less than a predetermined value, because the unequal time delays prevent the pulses from coinciding at the two AND gate inputs. But an output from the AND gate will be obtained when the frequency of the train of pulses equals a predetermined value at which the period of the train of fluid pulses substantially equals the difference in the time delays, so that coincidence of pulses does occur at the first and second inputs to the AND gate.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a block diagram of applicants invention;

FIG. 2 comprises two graphs of pertinent waveforms which illustrate the operation of the invention;

FIG. 3 is a schematic drawing of a preferred embodiment of the invention; and

FIG. 4 is a graph showing the frequency response of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral generally designates a fluidic frequency responsive switching circuit, according to the present invention. Circuit 10 comprises signal means 20, transmission means 30, and AND gate means 40. Signal means supplies a train of fluid pulses to transmission means 30. In one embodiment, signal means 20 may be a signal generator for generating a train of fluid pulses whose frequency is indicative of a variable quantity. In another embodiment, signal means 20 may be a conduit for supplying a train of fluid pulses to transmission means from another fluidic circuit, such as a control circuit, or the like. Fluid pulses from signal means 20 are applied to conduit 31 of transmission means 30. Conduit 31 branches into conduits 33 and 34 at junction 32. The other ends of conduits 33 and 34 are connected to inputs 43 and 44, respectively, of AND gate 40. Conduit 33 has a longer path length than conduit 34, so that a greater length of time is required for a pulse to pass through conduit 33 than through conduit 34. This follows from the fact that conduits 33 and 34 are filled with the same fluid at the same ambient pressure and temperature, so that the velocity of sound in the two conduits is the same. Therefore, the time required for a pulse to propagate through conduits 33- and 34 is proportional to their respective lengths; and the difference in propagation times for the two conduits is proportional tov the difference in their lengths. In FIG. 1, conduit 33 is shown as being of a coiled configuration, but it will be understood from the foregoing that a coiled shape, or any other particular shape is not necessary; it is only necessary that the path length of conduit 33 be greater than that of conduit 34.

AND gate is any type of logical AND gate, such as is well known in the art. AND gate 40 has first and second inputs and an output, indicated respectively by reference numbers 43, 44 and 45. AND gate 40 functions to produce a logical l signal at output only when logical l signals are present at both inputs 43 and 44. If a logical 0 signal is present at either one or both of the inputs 43 or 44, a logical 0 is produced at output 45. In the embodiment of the invention shown in FIG. 1, a logical l is represented by a high pressure condition, and a logical 0 is represented by a low, or ambient pressure condition. Conduit 51 connects output 45 to utilization means 50, the function of which is described herein in a subsequent paragraph.

The operation of the present invention as shown in FIG. 1 will now be explained with reference to FIG. 2. In FIG. 2, the horizontal axis represents time, and the vertical axis represents signal amplitude. Two separate graphs, A and B, show the operation of the invention in response to fluid pulses of two different frequencies. In graph A, waveforms 32a, 44a, 43a and 45a show the waveforms appearing at junction 32, inputs 44 and 43, and output 45, respectively, of FIG. 1. A train of fluid pulses of relatively low frequency is supplied by signal means 20, to conduit 31. A pulse arriving at junction 32. at time it, (see waveform 32a) is transmitted almost simultaneously to input 44 of AND gate 40 (see waveform 44a), the time delay introduced by conduit 34 being neglected for purposes of clarity. At the same time, the pulse begins to travel through conduit 33, but because of the delay caused by the greater length of conduit 33, the pulse does not arrive at input 43, until time The time delay A is indicated in graph A of FIG. 2 and is equal to the difference in transmission time between conduits 33 and 34. In other words, A t By time the pulse at input 44 has already terminated, so that no coincidence of pulses at inputs 43 and 44 occurs. Consequently, no output pulse appears at output 45-of AND gate 40, and the output waveform remains at a low pressure condition, as shown in waveform 45a.

The same pattern is repeated when the next pulse from signal means arrives at junction 32, and so on, with the net result that no output signal appears at output 45, when signal means 20 is supplying a relatively low frequency train of fluid pulses, as shown.

. Graph B of FIG. 2, shows the operation of the present invention when signal means 20 is supplying a train of fluid pulses of a predetermined frequency, which is higher than the frequency in the preceding example. The pulses arrive at junction 32, as shown in waveform 32b. The first pulse shown arrives at junction 32 at time 1 Almost simultaneously it is transmitted to input 44, as shown in waveform 44b (the time delay introducedby timeconduit 34 being neglected for clarity). At the same time the pulse begins to travel down conduit 33, but because of the time delay, A, it does not arrive at input 43 until time t.,. This is shown in waveform 43b. It will be noted from an examination of waveforms 44b and 43b that the delayed pulse arriving at input '43 coincides with the next succeeding undelayed pulse arriving at input 44. Consequently, an output pulse is produced at output 45 of AND gate 40. This result is shown at waveform 45b. It will beseen that the necessary condition for the production of an output pulse as illustrated by graph B is that the frequency of the applied train of pulses be such that its period equals the difference in time delays between the twoconduits 33 and 34. It will also be appreciated that if the frequency of the applied train of fluid pulses is increased further, the period would soon become sufficiently smaller than the time delay A so that pulses would no longer coincide at inputs 43 and 44, and consequently no pulses will be produced at output 45. Theoretically, it is possible for the frequency of the applied train of .fluid pulses to increase to a point at which the period of the pulses is one-half, one-third, etc. of the time delay A. At such frequencies, coincidence would still occur, but with one, two, etc. pulses in transit in conduit 33.

In addition to the examples given in the above paragraphs it will be appreciated that at certain very low frequencies, it may happen that output pulses will occur, depending upon the widths of the pulses involved. For example, at very low frequencies, lower than that shown in FIG. A, the widths of the pulses become greater than the time delay A. Pulses then overlap at inputs 43 and 44, and output pulses will be obtained. In normal operation, however, the invention of FIG. 1 is operated in ranges of frequencies corresponding to graphs A and B of FIG. 2.

The output of the invention shown in FIG. 1 as a function of frequency is shown in the graph of FIG. 4, in which the horizontal axis represents frequency, and the vertical axis indicates whether an output is obtained at output 45. In FIG. 4, in the range of very low frequencies designated as f,,, output pulses are obtained due to the overlap condition described in the preceding paragraph. In the range of frequencies designated as f the circuit of FIG. 1 operates as was described with reference to graph A of FIG. 2, and no output is obtained. At the frequency marked f coincidence of pulses occurs, as was described with reference to graph B of FIG. 2, and output pulses are obtained. At frequencies greater than f,,, no output is obtained until a frequency equal to twice f,, is obtained.

A useful application of the circuit of FIG. 1 is as follows. In a control system, it may be necessary to provide a fluidic circuit to prevent an overspeed of the turbine shaft of a gas turbine engine. In such a case, pulses whose frequency corresponds to turbine shaft speed are generated by, or supplied to, signal means 20. The length of conduit 33 is chosen so that A and fl, correspond to the maximum allowable turbine speed. Therefore, in normal operation the turbine shaft maintains the speed somewhere in the region designated f, in FIG. 4. If the speed of the turbine shaft should increase due to the onset of an overspeed condition, the frequency of the pulses supplied by signal means 20 would correspondingly increase until frequency fl, is reached. At frequency f,, output pulses are obtained at output 45, and are transmitted via conduit 51 to utilization means 50. In this example, utilization means 50 might be a fluid pulse responsive actuator which would be operable to reduce or cut off the fuel supplied to the engine. Thus, in this particular application, the circuit of FIG. 1 would function as a speed limiting switch.

A more detailed embodiment of the present invention is shown in FIG. 3. Reference numeral 20 generally designates signal means, or signal generating means, which comprises pulse wheel 21, shaft 22, nozzle 23, and receiver 24. Shaft 22 is rotated by variable speed driving means, not shown. Pulse wheel 21, which has an aperture near its circumference, is attached to shaft 22 for rotation therewith. Nozzle 23 and receiver 24 are axially aligned and spaced on either side of pulse wheel 21 so as to be in line with the aperture of the pulse wheel when it passes between them. Fluid at a working pressure is supplied to nozzle 23 by pressure source 15 and conduit 16. Fluid exiting nozzle 23 is normally prevented from entering receiver 24 by pulse wheel 21. However, as pulse wheel 21 rotates, its aperture becomes momentarily aligned with nozzle 23 and receiver 24, so that a pulse of fluid is received by receiver 24.

Transmission means 30 comprises trunk conduit 31, junction 32, and branch conduits 33 and 34. As in the embodiment of FIG. 1, conduit 33 provides a longer path length to a pulse supplied to conduit 31 and does conduit 34.

Reference numeral 40 of FIG. 3 generally designates one type of fluidic AND gate. The AND function is performed by bistable fluidic amplifier 41, which comprises power nozzle 47, outlet passages 45 and 46, and control ports 42, 43 and 44. Fluid at a working pressure is supplied to power nozzle 47 by pressure source 15, via conduit 16, which is a power supply conduit. Conduit 33 of transmission means 30 connects to control port 43, and conduit 34 connects to control port 44. A bias signal is applied to control port 42 by pressure source 15, through conduit 16 and restrictor 48.

The operation of bistable fluid amplifier 41 is well known in the fluidic art. Basically, the power stream issued by power nozzle 47 passes through the amplifier and out either outlet passage 45 or outlet passage 46, but not both simultaneously. The power stream tends to remain in an outlet passage due to the familiar lock on effect. The power stream can be switched over from one outlet passage to the other by means of a pressure differential applied across it by the control port s. In FIG. 3, the bias signal applied to control port 42 normally causes the power stream to pass through outlet passage 46, where it is vented to the atmosphere. Rcstrictor 48 is chosen to allow sufficient flow into control port42 so that the bias provided thereby may be overcome only by the application of pressure signals at bothcontrol ports 43 and 44 simultaneously. That is, a pressure signal at only one or the other of control ports 43 and 44 will not be strong enough to overcome the bias supplied to control port 42 so as to switch the power stream to outlet passage 45. Accordingly, the power stream may only be switched to outlet passage 45 when pressure signals are present at both control ports 43 and 44 simultaneously. v

The operation of the embodiment of FIG. 3 through outlet passage 45 is identical to the operation ofthe embodiment of FIG. 1, as explained above with reference toQFIGS. .1 and 2. Pulses generated by pulse wheel 21 are transmitted through conduit 31 to junction 32. At lower frequencies corresponding to graph A of FIG. 2, the pulsetraveling through conduit 34 arrives at control port 44 before the pulse traveling through conduit 33 arrives at control port 43 The single pulse at control port 44 is not sufficient to overcome the bias supplied to control port 42, and the output of fluid amplifier 41 remains in outlet passage 46. Atspeeds of rotation of shaft 22 corresponding to the higher predetermined frequency of pulses as in graph B of FIG. 2, pulses arrive in control port 44 and 43 substantially simultaneously, as has been described above with reference to graph B of FIG. 2. Pulses at both control ports 43 and 44 are sufficient to overcome the bias at control port 42 and to cause a pulse to appear at outletpassage 45.

The circuit of FIG. 3 also contains latching circuit means 70 for maintaining an output signal once the predetermined value of input speed has been reached. Latching circuit means 70 comprises bistable fluid amplifier 71 which comprises power nozzle 72, outlet passages 73 and 74, first control port pair 75 and 76, and second control port pair 77 and 78. Fluid at a working pressure is supplied to power nozzle 72 by conduit 16. A bias signal is applied through restrictor 79 to control port 76. Reset signals, the purpose of which is explained below, are applied to control port 78 by reset valve 82 and conduit 81. Output signals from outlet passage 74 are applied to utilization means 50 by conduit 51. Feedback signals from outlet passage 74 are supplied to control port 77 by conduit 84 and restrictor 83. Output signals from outlet passage 45 of amplifier 41 are applied to control port 75, of amplifier 71 by conduit 80.

Latching circuit means 70 operates as follows. Normally, in the absence of output signals from outlet passage 45 of amplifier 41, the power stream of amplifier 71 is biased to flow through outlet passage 73 by the bias signal applied to control port 76. The power stream of amplifier 71 remains in this position until a signal from amplifier 41 is applied to control port 75. This signal causes the power stream to switch to outlet passage 74, and thereby to flow through conduit 51 to utilization means 50. At the same time, output is fed back through restrictor 83 and conduit 84'to control port 77,which causes the power stream to remain in outlet passage 74 even after the pulse applied to control port has disappeared. In this manner, an output from amplifier 41 is held at conduit 51 by the action of the latching circuit. The latching circuit may be unlatched or reset by actuating reset valve 82, which allows fluid at a pressure from conduit 16 to pass through conduit 81 to control port 78, thereby overpowering the feedback signal applied to control port 77, to return the power stream to outlet passage 73.

Thus, the entire circuit of FIG. 3 operates as follows. Shaft 22 may be geared to a device or machine (not shown), the speed of which is to be'limited. Utilization means 50 may be a switch, valve, or other actuator operable to control the speed of the machine which drives shaft 22. At normal operating speeds, the speed of pulse wheel.21, and hence the frequency of pulses applied to conduit 31 is such that no output pulse is obtained at outlet passage 45. If the speed of rotation of shaft 22 increases to a predetermined value, coincidence of pulses occurs at control ports 43 and 44, output pulses appear at outlet passage 45, and the power stream of amplifier 71 is switched to outlet passage 74, thereby energizing utilization means 50.

I claim as my invention: I 1. A fluidic frequency responsive circuit, comprising: signal means for supplying a train of fluid pulses having a variable frequency; 5

fluid AND gate means having first and second inputs and an output, said fluid AND gate means for producing an output signal only during the time that fluid pulses are present at both said first and said second inputs;

conduit means connected to said signal generating means, said conduit means having first and second branches separating from a common junction and configured so that signals supplied to said conduit are transmitted simultaneously and with equal phase into both branches;

means connecting said first branch to said first input for conveying said fluid pulses thereto with a first time delay;

further means connecting said second branch to said second input for conveying said fluid pulses thereto with a second time delay which is greater than said first time delay, so that pulses are not simultaneously applied to said first and second inputs if said frequency is less than a predetermined value, and so that pulses are simultaneously applied to said first and second inputs thereby producing an output signal if said frequency equals said predetermined value, said predetermined value corresponding to that frequency at which the period of the train of fluid pulses substantially equals the difference in the time delays.

2. Apparatus according to claim 1 further including latching circuit means connected to said output means, said latching circuit means for maintaining an output signal once said predetermined value has been reached. 

1. A fluidic frequency responsive circuit, comprising: signal means for Supplying a train of fluid pulses having a variable frequency; fluid AND gate means having first and second inputs and an output, said fluid AND gate means for producing an output signal only during the time that fluid pulses are present at both said first and said second inputs; conduit means connected to said signal generating means, said conduit means having first and second branches separating from a common junction and configured so that signals supplied to said conduit are transmitted simultaneously and with equal phase into both branches; means connecting said first branch to said first input for conveying said fluid pulses thereto with a first time delay; further means connecting said second branch to said second input for conveying said fluid pulses thereto with a second time delay which is greater than said first time delay, so that pulses are not simultaneously applied to said first and second inputs if said frequency is less than a predetermined value, and so that pulses are simultaneously applied to said first and second inputs thereby producing an output signal if said frequency equals said predetermined value, said predetermined value corresponding to that frequency at which the period of the train of fluid pulses substantially equals the difference in the time delays.
 2. Apparatus according to claim 1 further including latching circuit means connected to said output means, said latching circuit means for maintaining an output signal once said predetermined value has been reached.
 3. The apparatus of claim 1 wherein said signal generating means comprises a pulse wheel assembly, whereby said fluid switching circuit operates as a speed sensing switch. 